Phytosterols are not only used in clinical administration etc. expected to have an effect of reducing cholesterols in blood but also utilized as raw or starting materials for medicines as substitutes for cholesterols or as emulsifiers or emulsion-stabilizers in cosmetics and foods.
Sterols are contained in vegetable fats and oils such as a soybean oil, a rapeseed oil, a rice bran oil, a palm oil, a palm kernel oil and a coconut oil. There has been practically used a producing process by extraction and/or purification thereof from a deodorized concentrate etc. generated upon purification of fats and oils. JP-B 52-8309 describes a general method of extracting therefor. The method comprises adding a lower alcohol to a deodorized distillate of fats and oils in order to esterify with an acid catalyst, then washing with water to remove the acid catalyst, adding an additional lower alcohol and an alkali catalyst to carry out a transesterification reaction, further being calmly left overnight to precipitate crystals, separating the crystals by filtration, and washing and drying with hexane, in order to obtain phytosterols. And, it is described that the purity of the obtained phytosterols is 82%. However, the purity of the purified phytosterols is too low to be used directly as pharmaceutical preparations and food additives.
When methanol is particularly used as the lower alcohol for an esterification or transesterification reaction, methyl esters of C6-28 fatty acids are contained as impurities in the resultant phytosterols. If these fatty acid methyl esters can be removed, a highly pure phytosterol can be obtained.
As a method of removing them, there is exemplified a saponification with an alkali. This method comprises converting a fatty ester with an alkali into a soap, precipitating a sterol crystal by cooling the soap, separating the crystal, and re-precipitating and drying the resultant crystal, in order to obtain a highly pure phytosterol. In this method, it is important how the saponification reaction is carried efficiently out, but, because of a low rate of saponification, the conventional method is not practical. Accordingly, the purification thereof by re-crystallizing repeatedly has been generally used in spite of an increasing number of steps. The problem of this method is that the yield of phytosterols is decreased thorough a number of steps, thus making the method uneconomical in respect of recovery.